Conventional modular conveyor belts and chains are constructed of modular links, or belt modules, arranged in rows. Spaced apart hinge eyes extending from each end of the modules include aligned openings. The hinge eyes along one end of a row of modules are interleaved with the hinge eyes of an adjacent row. A hinge rod, inserted in the aligned openings of interleaved hinge eyes, connects adjacent rows together end to end to form an endless conveyor belt capable of articulating about a drive sprocket or drum.
Because modular plastic conveyor belts do not corrode and are easy to clean, they are often used instead of metal belts. Usually, the hinge rods in plastic belts are also made of plastic. The hinge rods are typically circular in cross section and reside in circular openings in the hinge eyes. Relative motion between the hinge rods and the walls of the hinge eyes in the module as the belt articulates about sprockets or during other bending of the belt tends to wear both the hinge rod and the hinge eye wall. In abrasive environments, such as in conveying potatoes and other agricultural produce, this wear is accelerated by the intrusion of dirt and grit into the hinges of the belt.
Several solutions have been proposed to resist wear in module plastic conveyor belts. For example, non-circular hinge strips made of a flexible material and other approaches have been proposed to resist wear. Hinge eyes forming slots with flared ends permit the confined hinge strip to flex a limited angle without frictionally rubbing with the hinge eyes as the belt articulates. Such an arrangement is effective in increasing wear life, but the flexible hinge strip is inherently weak in shear strength and unsuitable for carrying heavy loads.
Metal hinge rods or hinge rods made of multiple materials have also been used to increase the wear life of the rods. But that does not do away with the relative motion between rod and hinge eye wall, and belt module wear at the hinge is still a problem.
U.S. Pat. No. 7,055,678 discloses a barrel-shaped hinge rod that is retained snugly in the hinge eyes along one belt row. The openings in the interleaved hinge eyes of the adjacent row are larger to allow the belt to articulate at the hinge between the adjacent rows. But the larger opening affords the hinge rod clearance that results in undesirable motion and rubbing of the rod against the walls of the larger openings.
Thus, there is a need for a modular plastic conveyor belt that can resist wear at the hinge for a long operating life even in abrasive environments.